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   On Sat, 02 Apr 2011 14:38:18 -0500, flipper  wrote:   
      
   >On Sat, 2 Apr 2011 02:55:54 -0700 (PDT), Patrick Turner   
   > wrote:   
   >   
   >>On Apr 2, 7:23 am, Newbie  wrote:   
   >>> It seems well known that negative feedback can reduce lower order   
   harmonics, but   
   >>> increase the higher order ones.   
   >>>   
   >>> Can anyone direct me to references that show how this happens with   
   mathematical   
   >>> analysis?  Perhaps a paper in the journal of the AES, or elsewhere; on the   
   web,   
   >>> perhaps?   
   >>   
   >>   
   >>During the last 40 years there have been at least two in depth   
   >>articles in Wireless World which later became Electronics World.  I   
   >>read all the WW and EW magazines from 1917 to about 1997 and you'll   
   >>probably find the articles you want to read if you go where there is   
   >>an archived set of the magazines like I did. In about 1993 I spent   
   >>days reading in several university library archives to see what had   
   >>been said about anything to do with audio engineering. Unfortunately I   
   >>don't have copies of all I read, but the phenomena of increasing   
   >>distortion spectra after applying NFB is well known, and remains   
   >>rivetted into my brain cells.   
   >>   
   >>The conditions required to "make matters worse" with NFB are about as   
   >>follows :-   
   >   
   >The only condition required to increase higher order harmonics is NFB.   
   >   
   Negative feedback can never make harmonics worse. Feedback can make   
   harmonics worse when the phase shifts far enough to make it positive.   
      
   d   
      
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